High-Toughness Tetragonal Zirconia/Alumina Nano-Ceramics

Abstract:

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The 0.75 to 3 mol% Y2O3-stabilized tetragonal ZrO2 and Al2O3/Y-TZP nano-composite
ceramics with 0.2 to 0.7 wt% of alumina were produced by a colloidal technique and low-temperature
sintering. The influence of the resulting density, microstructure, the yttria-stabilizer and the alumina
content on toughness was determined. The bulk 2.7Y-TZP ceramic with an average grain size of 110
nm reached fracture toughness of 11.2 MPa·m1/2. A nano-grained alumina/zirconia composite with an
average grain size of 92 nm was obtained. Y-TZP ceramics with a reduced yttria-stabilizer content
were shown to reach fracture toughness of 13.8 MPa·m1/2 (2Y-TZP), and 14.5 MPa·m1/2 (1.5Y-TZP).
Y-TZP/alumina composites with 0.35 wt% of Al2O3 were shown to reach fracture toughness of 15.7
MPa·m1/2 (2Y), 15.3 MPa·m1/2 (1.5Y).

Abstract: The fracture toughness is one of the requirements for mechanical properties of materials for use in satellites. The ceramic TZP zirconia (tetragonal zirconia polycrystals) have been investigated for applications in ballistic armor. Due to the chemical inertness and fracture toughness, this material has the potential to act as a screen against impacts of micrometeorites and space debris. The ceramic composites of alumina-zirconia 3Y-TZP (tetragonal zirconia polycrystals doped with 3 mol% ytria ) are the materials with the best benefit / cost for this application. This paper presents and discusses the results obtained from the use of two techniques for determining fracture toughness. The composite alumina - 18.5% of 3Y-TZP zirconia nanoparticles obtained from deflocculated powders have been tested for Vickers and the SEVNB penetration method (Single-Edge-Notch Beam V) to obtain the fracture toughness values (KIC). The KIC values obtained were analyzed due to the lower dispersion of experimental values. The SEVNB method showed better reliability in determining the toughness values in the studied ceramics.

Abstract: Alumina has been widely used as a structural ceramic because of high hardness and chemical stability. However, due to the unique characteristics of low fracture toughness of ceramic materials, it has seen limited use as a dynamic structural material. Recently, zirconia toughened alumina (ZTA) has been receiving spotlight, which has various toughness mechanisms caused by the volume change associated in the phase transformation process of ZrO2 particles dispersed in Al2O3 to increase the toughness of Al2O3. In this study, 8 mol% Y-ZrO2 and 12 mol% Y-ZrO2 with different crystal structures was dispersed in Al2O3 individually as a stabilizer and the mechanical properties of the ZTA were observed by differing the composition of the stabilizer. Experimental results show that the ZTA specimens with 12 mol% Y-ZrO2 which contains a large amount of stable cubic crystal phases had relatively higher micro hardness values. Whereas, fracture toughness of ZTA specimens with 8 mol% Y-ZrO2 which contains many unstable tetragonal crystal phases, was measured to have higher values than ZTA specimens with 12 mol% Y-ZrO2, which was opposite to that of micro hardness.